1. Field of the Invention
The present invention relates generally to an active matrix type liquid crystal display apparatus. More particularly, the invention relates a flicker lowering system in an active matrix type liquid crystal display apparatus.
2. Description of the Related Art
A drive method of a color display, in which one picture element consists of four pixels, is disclosed in Japanese Unexamined Patent Publication No. Heisei 3-78390, for example. An active matrix type liquid crystal display apparatus and a pixel structure is disclosed in Japanese Unexamined Patent Publication No. Heisei 3-78390 are illustrated in FIGS. 11 and 12.
In FIG. 11, L denote liquid crystal cells arranged in a matrix, C denote storage capacitors arranged in parallel to the liquid crystal cells, T denote field effect transistors (FET or TFT), each drain electrode of which is connected to one of electrodes of each liquid crystal cell L. Each pixel consists of these three elements.
X denote a plurality of X electrodes (data lines) commonly connected to input electrodes (source electrodes) of transistors per each column, in the matrix, Y denote a plurality of Y electrodes (gate line or scanning line) connected to gate electrodes of the transistors T in common per each row in the matrix, and Z denotes a common electrode commonly connected to other electrodes of all liquid crystal cells L. On the other hand, the reference numeral 100 denotes a scanning circuit sequentially applying scanning pulses to scanning lines Y, 200 denotes a driver circuit sampling/holding a video signal and converting the video signal equal to one horizontal line into parallel video signals of the number corresponding to number of data lines for supplying respective parallel video signals to respective data lines.
Referring to FIG. 12, a minimum picture element consists of four pixels of red (R), green (G), green (G) and blue (B) arranged in square matrix. Polarities of voltages to be applied to respective pixels are controlled so that a polarity of the voltage to be applied to one pixel region consists of a pair of red pixel and green pixel and a polarity of the voltage to be applied to the other pixel region consists of a pair of blue pixel and green pixel are opposite with respect to each other. In the alternative, a polarity of the voltage to be applied to one pixel region consists of a pair of green pixels and a polarity of the voltage to be applied to the other pixel region consists of a pair of red pixel and blue pixel are opposite with respect to each other.
FIG. 13 shows polarities of voltages to be applied to respective pixels in the case where the polarity of the voltage to be applied to one pixel region consists of a pair of red pixel and green pixel and a polarity of the voltage to be applied to the other pixel region consists of a pair of blue pixel and green pixel are opposite with respect to each other. On the other hand, FIG. 14 shows polarities of voltages to be applied to respective pixels in the case where the polarity of the voltage to be applied to one pixel region consists of a pair of green pixels and the polarity of the voltage to be applied to the other pixel region consists of a pair of red pixel and blue pixel are opposite with respect to each other. It should be noted that in FIGS. 13 and 14, the hatched portions represent the regions applied one polarity (e.g. positive or negative) of voltage and the blank portions (not hatched) represent the regions applied the other polarity (e.g. negative or positive) of voltage.
In the construction set forth above, when one color display of red is performed for an area perceptible by a human eye, for example, polarities of voltages to be applied per each field become the same with each other in all red pixels to inherently cause flicker irrespective of a pitch of the pixels. In the above-identified publication, discussion has been given for flicker lowering effect for yellow (green and red), cyan (green and blue), green (green and green) and magenta (red and blue). However, no discussion has been given for flicker lowering effect for red simple color.
In the above-identified publication, as an alternative embodiment, another pixel structure is illustrated in FIGS. 15 and 16. However, in either case, occurrence of flicker is inevitable in the case of red simple display. When the display is used as an output device of a computer, red simple display is frequently used. Therefore, it is highly possible to cause flicker.
A problem in the prior art set forth above, in such liquid crystal display apparatus, occurrence of flicker can be increased when particular simple color pattern is displayed, such as red simple color, for example. The reason is that a polarity of the voltage to be applied to the pixel is the same in respective pixels of red, green and blue to achieve cancellation effect when color matching with the polarity pattern is displayed.
It is therefore an object of the present invention to provide an active matrix type liquid crystal display apparatus which can reduce occurrence of flicker, which can be a cause of degradation of picture quality even in particular fixed pattern, by using a data driver circuit constantly inverting polarity of voltage of adjacent outputs.
According to the first aspect of the present invention, an active matrix type liquid crystal display apparatus comprises:
display picture elements, each consists of four pixels of first to four pixels arranged vertically and horizontally per two;
scanning lines, each being in common for the four pixels;
data lines arranged per two on opposite sides of vertically aligned two pixels;
a common electrode being common for the four pixels;
a data driver circuit for writing voltages from the data lines simultaneously for the four pixels of each picture element when the one scanning line is selected,
the pixels located at the same position in laterally adjacent picture elements being connected to data lines at different sides relative to each other; and
the data driver circuit being controlled to apply different polarities of voltages to adjacent data lines with respect to a voltage for the common electrode, and to invert polarities of the voltages to be applied to respective data lines with respect to the voltage of the common electrode when the scanning line is selected.
In the preferred construction, the data driver circuit performs control for inverting polarity with respect to the common electrode per frame.
According to the second aspect of the present invention, an active matrix type liquid crystal display apparatus comprises:
a plurality of mutually parallel data lines;
a plurality of mutually parallel scanning lines arranged perpendicular to the data lines;
field effect type transistors, each provided in the vicinity of each intersection of the data line and the scanning line;
pixel electrodes, each connected to the field effect type transistor;
a common electrode;
liquid crystal provided between the pixel electrodes and the common electrode, each four pixels forming one picture element;
a scanning circuit sequentially applying voltages to the scanning lines;
a data driver circuit receiving a display data and applying voltages corresponding to the display data for the data lines;
the display driver circuit controlling application of voltage so that polarities of the voltages to be applied to first, second, third and fourth pixels of a first picture element at an arbitrary position of a display portion relative to a voltage of the common electrode are the same polarity in the first and second pixels, the same polarity in the third and fourth pixels and opposite polarity in the first and third pixels;
so that polarities of voltages to be applied to the first to fourth pixels of the first picture element relative to the voltage of the common electrode are inverted at a period of a frame frequency;
so that polarities of voltages to be applied to fifth, sixth, seventh and eighth pixels located at the corresponding position to the first pixel in second, third, fourth and fifth picture elements adjacent to the first picture element in vertical and lateral directions are opposite to the polarity of the voltage to be applied to the first pixel;
so that the polarities of voltages to be applied to ninth, tenth, eleventh and twelfth pixels located at the corresponding position to the first pixel in sixth, seventh, eighth and ninth picture elements obliquely adjacent to the first picture element respectively located at obliquely upper left side, obliquely upper right side, obliquely lower left side and obliquely lower right side are the same as the polarity of the voltage to be applied to the first pixel.
In the preferred construction, the first, second, third and fourth pixels may display red, green, green and blue. In the alternative, the first, second, third and fourth pixels may display red, green, white and blue. In the further alternative, the first, second, third and fourth pixels may display white, respectively.
Discussing the operation of the present invention, each picture element in the display portion consists of four pixels. These four pixels are arranged to form a 2xc3x972 matrix. On opposite sides of each vertically aligned set of pixels, two data lines are arranged. Thus, a total of four data lines are arranged in each picture element. When one gate bus line is selected, voltages are written simultaneously for four pixels. The pixels laterally adjacent with each other are connected to data lines on opposite sides. Mutually opposite polarities of the voltages with respect to the voltage of the counter electrode (common electrode) are applied to adjacent data lines. The polarity of the voltage to be applied to each data bus line is inverted every time of sequential selection of the gate bus line.
As set forth above, one picture element consists of four pixels, and the combination of data bus lines to be connected to the pixels at the same positions in laterally adjacent picture elements are alternated for applying voltages to respective pixels in such a manner that the polarities of the voltages to be held during a certain frame period with respect to the voltage of the counter electrode in the pixels located at the same position as the pixel in one picture element, in the picture elements adjacent in vertical and lateral directions, are opposite to that held in the pixel of the one picture element. At the same time, within one picture element, the polarity of two pixels is positive and the polarity of the other two pixels is negative.
At this time, each pixel is adapted to perform color display. Assuming that the arrangement of colors in each picture element is the same, to the pixels of the same color in adjacent picture elements are applied mutually opposite polarities of voltages. Thus, variation of luminance can be canceled to avoid increasing of flicker even in display of fixed display pattern of simple color. Also, since one picture element consists of four pixels, and mutually opposite polarities of voltages are applied for respective pairs of two pixels, increasing of flicker can be avoided even in one picture element.